As an example of a conventional LED (light-emitting diode) substrate, Japanese Unexamined Patent Application Publication No. 2004-311791 (Patent Document 1) discloses such an LED substrate as illustrated in FIG. 5.
The LED substrate 10 of FIG. 5 has a concave portion 11a formed on the top surface of its ceramic substrate 11. Conductive wiring patterns 12 are formed on the concave portion 11a, and a single LED chip 13 is glued to the conductive wiring patterns 12 with its bottom surface facing the concave portion 11a (the bottom surface of the LED chip 13 is the surface through which light is not emitted). The electrodes on the light-emitting-surface side of the LED chip 13 are connected by wires 14, made of gold or the like, to particular locations of the conductive wiring patterns 12 on the concave portion 11a of the ceramic substrate 11. The concave portion 11a is sealed with resin 15 (e.g., silicone resin), or inert gas such as nitrogen or the like is sealed inside the concave portion 11a. Part of the side faces and part of the bottom face of the ceramic substrate 11 are covered with outer terminals 16 so that the LED substrate 10 can be electrically connected to other external devices. Note that multiple LED chips 13 with different luminescent colors can also be mounted on the concave portion 11a in place of the single LED chip 13.
As illustrated in FIG. 6, Patent Document 1 also discloses an LED light source that involves the use of multiple LED substrates 10, each of which is the one shown in FIG. 5. In this LED light source, the multiple LED substrates 10 are attached by solder 17a to the top surface of a substrate 17, made of glass epoxy resin or the like, in the form of a single or multiple rows. Also, an LED chip 13 (13a-13c) is mounted on each of the concave portions 11a-11c the LED substrates 10 with the bottom surfaces of the LED chips 13 facing the LED substrates 10.
When the LED light source of Patent Document 1 is used for a photolithography apparatus or an illumination device, sufficient heat release is required because the LED light source is driven by a high electric current. Thus, as illustrated in FIG. 6, a heat sink plate 18 is attached to the bottom surface of the substrate 17, i.e., the surface opposite the surface to which the substrates 10 are attached. This LED light source is arranged, as illustrated in FIG. 7, across from a light guide plate 19 of a backlight so that the light from the LED substrates 10 can travel into the light guide plate 19.
As another heat release structure, Patent Document 1 also discloses such an LED light source structure as illustrated in FIG. 8. In this LED light source, an LED chip 13 is glued to the conductive wiring patterns on each of concave portions 11a of ceramic substrates 11, with the bottom surfaces of the LED chips 13 facing the concave portions 11a. Also, a heat sink plate 18 is glued directly to the bottom faces of the ceramic substrates 11, i.e., the surface opposite the light emitting surface of the ceramic substrate. This LED light source also has a substrate 17 placed on the ceramic substrates 11. The substrate 17 has windows 21 so that the light emitted from the ceramic substrates 11 can travel there through. The conductive wiring patterns on the substrate 17 (not illustrated) which are used for power supply to the LED chips 13 are connected by solder 20 to the conductive wiring patterns on the top surfaces of the ceramic substrates 11 (not illustrated).
The LED display device of Patent Document 1 that involves the use of such LED light sources as above is capable of releasing the heat of the LED chips 13 efficiently because the heat can be transferred to the heat sink plate 18 only through the ceramic substrates 11 and the adhesive that glues the LED chips 13 to the ceramic substrates 11.
As a modification example of the LED substrate 10 of FIG. 5, Japanese Unexamined Patent Application Publication No. 2008-172177 (Patent Document 2) discloses, as illustrated in FIG. 9, a heat release structure in which a metal housing 22 the houses a liquid-to-vapor heat release device 23 is attached to the bottom surface of an LED chip 13, i.e., the surface opposite the light emitting surface of the chip 13.
In the heat release structure of Patent Document 2, the heat of the LED chip 13 can be quickly released through the metal housing 22 and the liquid-to-vapor heat release device 23, which is high in thermal conductivity. Thus, temperature rises of the LED chip 13 can be prevented.
Further, Japanese Unexamined Patent Application Publication No. 2006-250982 (Patent Document 3) discloses a maskless photolithography apparatus.